Oxidative rearrangement of aryl ethyl ketones to alkyl 2-arylpropanoates by lead(IV) acetate

Abstract

Treatment of the propiophenones p-R′C₆H₄COCH₂Me (1; R′= H, Me, Buⁱ, Ph, Br) with lead(IV) acetate in trialkyl orthoformate in the presence of acid catalyst is found to give alkyl esters of 2-arylpropanoic acids (2) in good to excellent yields via 1,2-aryl migration in (1). Hydrolysis of (2) leads to the corresponding acids, some of which are important pharmaceutical compounds. The rate of aryl migration increases when the substituent R′ is an electron-releasing group such as methyl, isobutyl, or phenyl. The rate of rearrangement of the dimethyl acetals of (1; R′= H, Buⁱ, Ph) is nearly the same as that of (1). Such rearrangement hardly occurs in the absence of acid catalyst. A reaction pathway involving the formation of a monoalkoxylead(IV) compound, and its decomposition accompanied with aryl migration is discussed.